Author: Robert Hyatt
Date: 08:40:22 08/26/03
Go up one level in this thread
On August 26, 2003 at 03:13:00, Johan de Koning wrote: >On August 25, 2003 at 18:28:24, Robert Hyatt wrote: > >>On August 25, 2003 at 18:14:15, Sune Fischer wrote: >> >>> >>>>(status quo). >>> >>>Right, saw that one too late :) >>> >>>>That is exactly what I said. The issue is how many copy/makes have to be >>>>done per unit of time. Or how many units of time it takes to do a single >>>>copy/make. Depends on your time scale (1s or 1ns). >>>> >>>>A single cpu that will run crafty at 1M nps has a cache-cache and cache-memory >>>>bandwidth of X bytes/second. A single cpu that runs crafty at 2M nps has >>>>exactly twice the cache-cache and cache-memory bandwidth and twice the clock >>>>frequency. A dual-cpu just needs two cpus, but the two cpus give twice the >>>>cache-cache bandwidth, but _no_ improvement in cache-memory bandwidth. >>>> >>>>This was all about memory bandwidth with respect to copy/make. >>> >>>Aaah, and here lies our source of disagreement. >>> >>>I was always talking about cache to cache, or as Johan wrote "C2C" bandwidth. >>> >>>I think the assumptions for make/uncopy to match make/umake is that the stack >>>fits in cache, or else it will be heavily outgunned, even on a single. >>> >>>I doubt anyone disagrees with you there. >>> >>>>> >>>>>You made it sound like 2.4 was much worse than 1, which is just a silly >>>>>comparison at best. >>>> >>>>Clearly 2.4 _is_ much worse than 1. It requires 2.4X the bandwidth. >>> >>>Yes _if_ you need to go over the bus. >>> >>>-S. >> >> >>My stuff will _never_ fit in 512KB of L2, much less the far smaller L1/trace >>caches (on the PIV). >> >>I am _always_ going to be burning the bus. > >Exactly! >The heavily used stuff will *always* be in the cache. >For the other stuff it doesn't matter much if the remaining cache space is >either 31 kB or 28 kB, now does it? > >... Johan I don't remember saying that id did matter. I claimed that for _my_ program, copy/make burned the bus up and getting rid of it made me go 25% faster. I didn't suggest that it would make any other program go 25% faster or slower, because other programs are likely very different internally.
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